System for cooling cooling air in a gas turbine, and method for cooling cooling air

ABSTRACT

Disclosed is a gas and steam turbine plant comprising a cooling system which is configured such that said cooling system is suitable for each operational state and cools cooling air that is bled from the compressed air, and a heat exchanger system which is mounted on the primary side of a cooling air duct that branches off the compressed air duct. Said heat exchanger system transmits heat that is transported in the cooling air to a flow of combustible gas which is fed to the combustion chamber of the gas turbine.

The invention relates to a cooling system for cooling down the coolingair which is tapped off from the compressor air in a gas turbine. Italso relates to a method for cooling the cooling air.

In a gas and steam-turbine system, the heat which is contained in theexpanded working medium (exhaust gas) from the gas turbine is used togenerate steam for the steam turbine. The heat is transferred in a wasteheat

steam generator which is connected downstream from the gas turbine onthe exhaust gas side and in which heating surfaces in the form of tubesor tube groups are arranged. These are in turn connected to thewater/steam circuit of the steam turbine.

The steam which is generated in the waste heat steam generator issupplied to the steam turbine, where it is expanded producing work. Thesteam which is expanded in the steam turbine is normally supplied to acondenser, where it is condensed. The condensate which is produced fromthe condensation of the steam is supplied once again as supply water tothe waste heat steam generator, thus resulting in a closed water/steamcircuit.

In order to increase the power of the gas turbine and thus to achieve agas and steam-turbine system such as this whose efficiency is as high aspossible, it is desirable for the exhaust gas or the combustion gases tobe at a particularly high temperature of, for example, 1000° C. to 1200°C. when they enter the gas turbine. However, a turbine inlet temperaturethat is as high as this results in material problems, particularly withregard to the heat resistance of the turbine blades.

The turbine inlet temperature cannot be increased unless the turbineblades are cooled sufficiently that they are always at a temperaturethat is below the maximum permissible material temperature. In thiscontext, it is known from EP-PS 0 379 880 for a flow element to betapped off from compressed air as it flows out of the compressorassociated with the gas turbine, and for this flow element to besupplied as a cooling medium to the gas turbine. The air which is usedas a cooling medium is cooled before it enters the gas turbine. In thiscase, an auxiliary steam generator, which is also referred to as akettle boiler, absorbs heat which has been extracted from the compressorair and is used, for example, to vaporize water, is normally used whenthe system is in the gas and steam mode. The steam which is producedduring this process is fed into the steam circuit.

However, this auxiliary steam generator is not available when the steamcircuit of the system is not in operation. When the system is being usedin the pure gas turbine mode, a comparatively large air cooler, which isalso referred to as a fin fan cooler, is therefore normally used as analternative to cool down the cooling air.

Switching from the pure gas-turbine mode to the gas and steam-turbinemode therefore also requires switching between the cooling systems forthe cooling air in each case. The cooling down process, which is notensured continuously owing to the switching process, means that it maynot be possible to avoid a load reduction, or even disconnection of theload from the system, when changing from the pure gas-turbine mode tothe gas and steam mode.

The invention is thus based on the object of specifying a gas andsteam-turbine system cooling system which is suitable for extraction ofheat from the cooling air and which can be set flexibly to the operatingstate of the gas and steam turbine with little hardware complexity. Afurther aim is to specify a method for cooling the cooling air which issuitable for different system operating conditions.

With regard to the cooling system, this object is achieved according tothe invention in that a heat exchanger system, which is connected on theprimary side is connected in a cooling air line that is tapped off fromthe compressor air line, transfers heat that is carried in the coolingair to the combustion gas flow which is supplied to the combustionchamber of the gas turbine.

The invention is in this case based on the idea that reliable coolingdown of the cooling air should be ensured irrespective of any heatintroduced into the water/steam circuit in the steam turbine in acooling system which can be flexibly matched to the operating state ofthe gas and steam turbine system. For this purpose, the cooling systemshould transfer heat extracted from the cooling air while it is beingcooled down to a medium which is available in every operating state ofthe system. One medium which is particularly suitable for this purpose,whose heating allows heat to be introduced into the actual powergeneration process, and thus also allows a particular improvement inefficiency, is the combustion gas flow which is supplied to thecombustion chamber.

Advantageous refinements of the invention are the subject matter of thedependent claims.

The amount of heat which has been extracted from the cooling air flowfor reliably cooling down the cooling air is generally greater than thatrequired to preheat the combustion gas, that is to say based on thenormal dimensions of gas and steam-turbine systems. The amount of heatsupplied to the combustion gas flow is thus advantageously variable.This ensures that an adequate amount of heat is always available forpreheating the combustion gas, and that the remaining amount of heat isdissipated in some other way.

In one preferred refinement, a heat dissipation capability from thecooling air which can be flexibly matched to the operating state of thesystem is achieved by splitting the heat flow dissipated from thecooling air into flow elements, one of which is supplied to thecombustion gas flow and another of which is used, for example, togenerate steam which can be supplied to the steam turbine. The splitinto flow elements is in this case carried out taking account of thecondition that the flow element which is supplied to the combustion gasflow carries with it precisely that amount of heat which is required forpreheating of the combustion gas, while the further flow element or flowelements dissipate the heat which is not required to preheat thecombustion gas or use it in some other way, for example for generationof auxiliary steam. The heat flow can be split by connecting a number ofintermediate circuits in parallel on the heat flow side. This results inheat dissipation capabilities in each intermediate circuit, so that thecooling system can be used particularly flexibly.

In a further alternative embodiment, whose hardware is particularlysimple, the heat exchanger system may have a heat exchanger whosesecondary side is connected directly in the combustion gas flow, andwhich transfers heat from the cooling air flow to the combustion gasflow.

If already existing components of the gas and steam-turbine system, suchas heat exchanger or auxiliary steam generator, are used, as may bedesirable by way of example in the case of retrofitting or upgradingmeasures, then the heat is expediently transferred via at least oneintermediate circuit, via which the secondary side of an auxiliary steamgenerator, which is also referred to as a kettle boiler, is connected toa heat exchanger, with the secondary side of the latter being connectedin the combustion gas flow. The configuration of the cooling system canthus be matched to the characteristics of the already existing system,thus saving technical complexity.

If necessary, a further auxiliary steam generator can also be connectedin the intermediate circuit and uses the heat to be dissipated togenerate auxiliary steam which is required in the system.

In one alternative refinement, the heat-side connection of the heatexchanger system to the further heat exchanger can be provided via theauxiliary steam generator, with the intermediate circuit thus being intwo stages. This provides further heat extraction and usage options, andmakes the cooling system particularly flexible. Apart from this, atwo-stage intermediate circuit allows more design and adaptation optionsand matching options for the cooling system to existing characteristicsand components.

With regard to the method, the object is achieved by heat which has beenextracted from the cooling air flow being transferred to the combustiongas flow which is supplied to the combustion chamber of the gas turbine.

In order to ensure optimum use of the heat contained in the cooling air,the amount of heat which is supplied to the combustion gas flow isadvantageously matched to the operating state of the gas turbine system.

For this purpose, the cooling air flow which is tapped off from thecompressor air is advantageously split into a number of flow elements,one of which supplies the combustion gas flow with the amount of heatrequired to preheat the combustion gas.

In one particularly simple refinement option, the amount of heat whichis provided for preheating the combustion gas is expediently transferredvia a heat exchanger whose secondary side is connected directly in thecombustion gas flow.

As an alternative to this, a single-stage or even a two-stageintermediate circuit may also be provided. This is particularlyexpedient when components which already exist in the cooling system,such as heat exchangers or auxiliary steam generators, are intended tobe used. In this situation, an intermediate circuit allows the heat flowto be split more flexibly into flow elements, and allows alreadyexisting components to be connected more flexibly.

In order to allow optimum use of the heat which is dissipated from thecooling air, an auxiliary steam generator is expediently connected inone of the flow elements which are not supplied to the combustion gasflow. This auxiliary steam generator uses the excess amount of heat asvaporization heat for generation of auxiliary steam that is required inthe system, and thus contributes to increasing the efficiency of thesystem.

The advantages achieved by the invention are, in particular, thattransferring at least a portion of the heat extracted from the coolinggas flow to the combustion gas flow increases the efficiency of the gasand steam-turbine system in the pure gas-turbine mode by saving externalpreheating sources. Since a significant proportion of the heat extractedfrom the cooling air when cooling it down can be reliably dissipatedcan, furthermore, be reliably dissipated via the combustion gas flow inany case, irrespective of the operating state of the steam turbine, thisallows switching from the pure gas-turbine mode to the gas and steammode without the previously unavoidable load reduction or loaddisconnection. Furthermore, there is no need for various componentswhich occupy a large amount of space, such as external heating gaspreheaters and the comparatively large air cooler, which is alsoreferred to as a fin fan cooler.

One exemplary embodiment of the invention will be explained in moredetail with reference to a drawing, in which:

FIG. 1 shows, schematically, a cooling system for cooling the coolingair for a gas turbine,

FIG. 2 shows a cooling system with an intermediate circuit,

FIG. 3 shows an alternative embodiment of the cooling system with anintermediate circuit,

FIG. 4 shows a further alternative embodiment of the cooling system withan intermediate circuit,

FIG. 5 shows a cooling system with a two-stage intermediate circuit, and

FIG. 6 shows a cooling system with natural circulation and with twointermediate circuits.

Identical parts are provided with the same reference symbols in all ofthe figures.

The gas turbine system 1 shown in FIG. 1 is part of a gas andsteam-turbine system which is not illustrated in any more detail. Thegas turbine system 1 has a turbine 2, which is preceded by a compressor4 and a combustion chamber 6. In addition, further combustion chambersmay also be provided. The or each combustion chamber 6 can be suppliedvia a line 8 and thus via the combustion air path with compressed air Vfrom the compressor 4 as combustion air. On the output side, thecombustion chamber 6 is connected via a line 10 or an additionalconnection to the turbine 2. The turbine 2 can in this case be suppliedvia the line 10 with hot exhaust gas, which has been produced bycombustion of a fuel. The turbine 2 and the compressor 4 are connectedto one another via a turbine shaft 12. The turbine 2, the compressor 4,the combustion chamber 6, the lines 8, 10 and the turbine shaft 12 arealso referred to in their totality as a gas turbine. The compressor 4 isalso connected to a generator 16 via a further shaft 14.

The gas turbine system 1 is designed for as high an efficiency aspossible. High efficiency is in this case achieved in particular by ahigh inlet temperature of the exhaust gas into the turbine 2. A highturbine inlet temperature such as this results, however, in materialproblems, in particular with respect to the heat resistance of theturbine blades. In order to avoid these problems, the turbine blades arecooled sufficiently to ensure that they are always at a temperaturebelow the permissible material temperature.

The turbine can be supplied as cooling air K with a flow element whichis tapped off from the compressor air V in order to cool the stationarystator blades (which are not illustrated in any more detail) and therotor blades, which are likewise not illustrated in any more detail butwhich rotate with the turbine shaft 12. For this purpose, the input endof a cooling air line 17 is connected to the line 8 downstream from thecompressor 4. On the output side, the cooling air line 17 is connectedto the turbine 2, so that the air which is intended as cooling air K canbe supplied to the stator blades and to the rotor blades of the turbine2.

In order to cool down the compressed air V, which is intended to be usedas cooling air K, a cooling system 18 which comprises a heat exchangersystem 21 connected in the cooling air line 17 and having at least oneheat exchanger 22 is used. The heat exchanger 22 may in this case be anauxiliary steam generator, which is also referred to as a kettle boiler,and a cooling medium, in particular water, can be applied to itssecondary side. The heat exchanger 22 is in this case designed inparticular such that the medium to be cooled, that is to say the hotcompressor air or compressed air V, is passed through a large number oftubes, while the cooling medium (water) is being supplied, and isgenerally vaporized.

The cooling system 18 is designed for particularly high systemefficiency, with high flexibility at the same time. To this end, thecooling system 18 is designed to transfer heat carried in the coolingair K to the combustion gas flow 23, so that this heat can be used topreheat the combustion gas. This avoids the need for the externalcombustion gas preheater and components for cooling the cooling air K.Furthermore, this cooling system 18, which is suitable for all theoperating states of the gas and steam-turbine system, means that thereis no need for any load reduction or load disconnection while switchingfrom the pure gas-turbine mode to the gas and steam mode.

In the exemplary embodiment shown in FIG. 1, the primary side of theheat exchanger 22 is for this purpose connected directly in the coolingair line 17, and its secondary side is connected directly in acombustion gas line, which is intended to carry the combustion gas flow23. In this case, the heat is transferred from the cooling air K to thecombustion gas flow 23 by only a small number of components. However,with a conventional system design, it would be possible to take accountof the fact that the amount of heat which can be extracted from thecooling air K for reliable operation of the turbine 2 is greater thanthe amount of heat which can be transferred, by virtue of the design, tothe combustion gas flow 23. For example, it may be necessary to extractfrom the cooling air K an amount of heat which corresponds to a heatingpower of about 7 MW while, in contrast, a maximum amount of heatcorresponding to a heating power of about 3 MW can be transferred to thecombustion gas flow 23. In order to take account of this aspect, theexemplary embodiment envisages only partial transfer of the heatextracted from the cooling air K to the combustion gas flow 23, with theremaining heat which still has to be dissipated in addition to thisbeing transferred to other media.

In order to ensure such distribution of the heat extracted from thecooling air K as required, the exemplary embodiment shown in FIG. 1provides for the cooling air flow that is to be cooled down to be splitinto two flow elements. For this purpose, a further heat exchanger 24 isconnected in parallel with the heat exchanger 22 in the heat exchangersystem 21. The cooling air flow is thus split into two flow elements,with the first flow element being passed via the cooling air line 17 andvia the heat exchanger 22, and the second flow element -being passed viabranch line 26, which is tapped off from the cooling air line 17, andvia the further heat exchanger 24.

In this order in this case also to ensure that the heat extracted fromthe cooling air K is dissipated in a form matched to the operating stateof the system and that the heat exchanger 22 is supplied with heat, theflow elements in the cooling air line 17 and in the branch line 26 are,furthermore, variable by means of fittings that are not illustrated inany more detail. The further heat exchanger 24 dissipates the heat thatis not required to preheat the combustion gas and supplies it foranother suitable purpose, for example as vaporization heat.

FIG. 2 shows an alternative embodiment option for the cooling system 18.In this exemplary embodiment, the heat exchanger system 21 is designedto transfer heat indirectly from the cooling air K to the combustion gasflow 23 with the interposition of an intermediate circuit 32. In thiscase, the cooling air K which is tapped off from the compressor air V ispassed through the cooling air line 17 and via the first heat exchanger22. The secondary side of the heat exchanger 22 is connected in theintermediate circuit 32. A further heat exchanger 33 is connected in theintermediate circuit 32, and transfers heat to the combustion gas flow23, in order to preheat the combustion gas. A separating bottle 34,which is connected downstream from the further heat exchanger 33 in theintermediate circuit 32, supplies the heat exchanger 22 with the mediumwhich transfers the heat, for example water, again. Furthermore, wateror steam can be tapped in from the separation bottle 34 and can besupplied, for example, to an auxiliary steam generator, which is notillustrated in any more detail, or to loads.

In order also to allow the possibly desirable splitting on the heat flowside into a number of flow elements in this exemplary embodiment, theheat exchanger 22 may also be designed to have a number of componentsand, for example, may have a segment in the form of an auxiliary steamgenerator or kettle boiler, via which a proportion of the heat issupplied for another purpose. This is represented by the heating coil 5in FIG. 2.

The embodiment option illustrated in FIG. 2 allows the heat extractedfrom the cooling air K to be dissipated and distributed in aparticularly flexible form via the intermediate circuit 32. Furthermore,the intermediate circuit 32 allows physical decoupling of the majorfunctions, specifically on the one hand the heat dissipation from thecooling air K, and on the other hand the heat transfer to the combustionair flow 23. This decoupling allows the use of components which alreadyexist in the system, such as heat exchangers, auxiliary steam generatorsor a cooling circuit, in which case all that is necessary is to adaptthe line routing. This concept is therefore particularly suitable forupgrading already existing systems.

A further variant of the cooling system 18 is illustrated in FIG. 3. Inthis variant as well, the heat exchanger system 21 includes the heatexchanger 22, whose primary side is connected in the cooling air line 17and whose hot side is connected to a further heat exchanger 33 via anintermediate circuit 32. Thus, in this variant as well, heat istransferred to the combustion gas via the intermediate circuit 32 andvia the further heat exchanger 33, whose secondary side is connected inthe combustion gas flow 30. In contrast to the connections shown in FIG.2, the secondary side of the heat exchanger 22 is, however, in this caseconnected only in the intermediate circuit 32. A third heat exchanger 36is in this case provided in order to split the heat flows as required,whose primary side is connected in series in the cooling air line 17downstream from the heat exchanger 22 and can thus absorb heat whichstill remains in the cooling air K. The secondary side of the third heatexchanger 36 is connected to components which are suitably chosen toabsorb the remaining heat. This circuit has the particularlyadvantageous feature that the only task of the third heat exchanger 36is to dissipate the excess heat which cannot be used in the combustiongas flow 23, as is possibly the case in gas and steam-turbine systems.Generally speaking, there is therefore no need to modify or replaceexisting components.

FIG. 4 illustrates a further embodiment, which is likewise based on theuse of an intermediate circuit 32. In this case, the cooling air K iscooled down via the third heat exchanger 36 even before it enters theheat exchanger 22. The intermediate circuit 32 is in this case designedto use water/steam as the medium for transferring heat to the furtherheat exchanger 33. In this case, the heat exchanger 22 is for thispurpose designed as a steam generator. In this case, the amount of heattransferred in the heat exchanger 22 is varied as required by means ofthe third heat exchanger 36.

An embodiment is also feasible, as illustrated in FIG. 5, in which theheat is transferred from the cooling air K to the combustion gas flow 23via a two-stage intermediate circuit system 40. In this intermediatecircuit system 40, the heat exchanger 22, whose primary side isconnected in the cooling air line 17, transfers heat from the coolingair K to a medium which is carried in a first intermediate circuit 42.The primary side of a further heat exchanger 44 is connected in theintermediate circuit 42, and once again transfers heat to a medium whichis carried in a second intermediate circuit 46. Finally, the primaryside of the heat exchanger 48 is connected in the second intermediatecircuit 46, and transfers heat to the combustion gas flow.

This embodiment has the advantage that the dissipation and use of theheat extracted from the cooling air K can be configured particularlyflexibly. In particular, there is a large number of options for the linerouting and for the connection of further heat loads as required, sothat it is also possible to use existing system components in aversatile form. For example, a portion of the heat which is not requiredto preheat the combustion gas can be used in an auxiliary steamgenerator 50, which is connected downstream from the heat exchanger 48in the second intermediate circuit 46, to generate auxiliary steam whichis required in the system. Heat which is not required can be dissipatedvia an air cooler which is not illustrated in any more detail.Furthermore, like the embodiment based on a single-stage intermediatecircuit, this embodiment offers a large number of options for the useand connection of components which already exist in the system.

The water/steam mixture that is carried in the intermediate circuit 32may in this case be connected to the water/steam circuit for the gas andsteam-turbine system at different, suitably chosen points in order toprovide a particularly high degree of operational flexibility.

FIG. 6 shows an exemplary embodiment in which the rotor air cooling andthe heating gas preheating are largely integrated in already existingpower station components. In this case, the cooling air K is suppliedvia the cooling air line 17 to the heat exchanger 22, which is in theform of a kettle boiler, with the required amount of heat beingdissipated by vaporization. The steam which is generated on thesecondary side in this case can either be supplied to the heat exchanger44 (which is in the form of a condenser) in the intermediate circuitsystem 40, or can be supplied to another load in the power station viathe auxiliary steam line 52. The intermediate circuit system 40 may inthis case in particular be designed as a natural circulation system,with the secondary side of the heat exchanger 44 itself being connectedto a cooling-down system 51. A portion of the medium flow from the heatexchange 22, which carries the amount of heat required for heating gaspreheating, is passed via a line 54 and via the heat exchanger 33, whosesecondary side is connected in the combustion gas flow 23, and then backagain into the heat exchanger 22.

Inclusion of the media side in further existing systems is illustratedby way of example by the feed water line 37. A circuit such as thisallows all the methods of operation in the gas-turbine mode or in thegas and steam-turbine mode for heating gas combustion or firing. In thiscase, the functionality of the rotor air cooling remains unaffected inall operating states, even when using a second fuel (for example heatingoil)—that is to say without operation of the heat exchanger for heatinggas preheating. The present concept is also particularly suitable forretrofitting and conversion of gas-turbine systems by the addition ofheating gas preheating, and thus in order to increase the efficiency.Owing to the wide range of connection options which are feasible on thehot side, this is likewise also particularly advantageous forretrofitting a gas-turbine system, to form a gas and steam-turbinesystem.

1-15. (canceled)
 16. A cooling air cooling system in a power generationstation, comprising: a gas turbine having a compressor component, acombustion component, and a turbine component; a cooling air line with aprimary side; cooling air extracted through the cooling air line from avolume of compressor air; and a heat exchanger system connected towardthe primary side of the cooling air line and receives a portion of thecooling air, wherein the heat exchanger system transfers heat that iscarried in the cooling air to a combustion gas flow which is supplied tothe combustion chamber of the gas turbine.
 17. The cooling system asclaimed in claim 16, wherein the amount of heat supplied to thecombustion gas flow is changeable.
 18. The cooling system as claimed inclaim 16, wherein the heat exchanger system has a secondary side. 19.The cooling system as claimed in claim 16, wherein the heat exchangersystem is connected on the secondary side of a number of circuitelements which are connected in parallel on the heat flow side.
 20. Thecooling system as claimed in claim 16, wherein the heat exchanger systemcomprises a heat exchanger with a secondary side that is connecteddirectly in the combustion gas flow.
 21. The cooling system as claimedin claim 16, wherein the heat exchanger system is connected on thesecondary side via an intermediate circuit to a further heat exchangerthat is connected on a secondary side in the combustion gas flow. 22.The cooling system as claimed in claim 21, via whose intermediatecircuit an auxiliary steam generator can be heated.
 23. The coolingsystem as claimed in claim 22, wherein a connection on a heat side ofthe heat exchanger system to the further heat exchanger is produced viaan auxiliary steam generator.
 24. A method for cooling a volume ofcooling air for a gas turbine, comprising: removing a portion of airflow as cooling air flow from a compressor; extracting heat from thecooling air flow; and transferring the extracted heat to a combustiongas flow and supplying the flow to a combustion chamber of the gasturbine.
 25. The method as claimed in claim 24, wherein the amount ofheat supplied to the combustion gas flow is matched to the operatingstate of the gas turbine system.
 26. The method as claimed in claim 24,wherein the heat flow extracted from the cooling air is divided andsupplied to a number of flow elements.
 27. The method as claimed inclaim 24, wherein the heat is transferred via a heat exchanger with asecondary side that is connected directly in the combustion gas flow.28. The method as claimed in claim 24, wherein heat is transferred froma cooling air line to the combustion gas flow via an intermediatecircuit.
 29. The method as claimed in claim 28, wherein an amount ofheat is transferred to an auxiliary steam generator that is connected inthe intermediate circuit.
 30. The method as claimed in claim 24, whereinin a first circuit an amount of heat is transferred from the cooling airflow a first heat exchanger to an auxiliary steam generator which isconnected in a first circuit and is transferred to the combustion gasflow by a further heat exchanger.